Such ball-joint assemblies have been employed for a long time in the aeronautical industry with a view to constituting links for connecting rods or other control members.
Up to the present time, as described in British Patent GB-2 170 279.B, an outer ring has been used, whose spherical concave surface is coated with polytetrafluoroethylene, whilst the ball which cooperates with the ring is coated with a thin layer of very hard matter such as tungsten carbide.
As the ball comprises two flattened poles, there are two sharp circular edges between the two flat portions and the spherical central part of the ball. As it is only this central part which is coated with a hard layer such as tungsten carbide, considerable irregularities or flakings frequently occur both during manufacture and during use of the pieces, at the level of the connection of the spherical central part and the two faces. Chipping of the hardened surface leads to the piece in question being discarded, as it is inacceptable to use it as such. Such discarding involves high dismantling and re-assembly costs particularly if the defects are produced during assembly of the articulation.
It is an object of the improvements forming the subject matter of the present invention to overcome these drawbacks and to enable a ball with two flattened poles to be produced, which presents no risk of deterioration of the layer of matter added at the level of connection of this layer and the lateral faces of the ball.